Evaluation of the Effectiveness of ST266 Ophthalmic Drops Compared to Placebo to Treat Allergic Conjunctivitis

Inclusion Criteria: * be at least 18 years of age of either gender and any race; * provide written informed consent and sign the HIPAA form; * be willing and able to follow all instructions and attend all study visits; have a positive history of ocular allergies and a positive skin test reaction to a seasonal AND perennial allergen as confirmed by an allergic skin test; * be able and willing to avoid all disallowed medication for the appropriate washout period and during the study; * be able and willing to discontinue wearing contact lenses for at least 72 hours prior to and during the study trial period; * (for females capable of becoming pregnant) agree to have urine pregnancy testing performed at screening (must be negative) and at the study exit; must not be lactating; and must agree to use a medically acceptable form of birth control throughout the study duration and for at least 14 days prior to instillation of investigational product). Women considered capable of becoming pregnant include all females who have experienced menarche and have not experienced menopause (as defined by amenorrhea for greater than 12 consecutive months) or have not undergone successful surgical sterilization (hysterectomy, bilateral tubal ligation, or bilateral oophorectomy); * have a calculated visual acuity of 0.7 logMAR or better in each eye as measured using an ETDRS chart; * have a positive post-CAC reaction; * have a positive post-CAC reaction in two out of the first three time points; * be able to self-administer eye drops satisfactorily or have a caregiver at home routinely available for this purpose. Exclusion Criteria: * have known contraindications or sensitivities to the use of the investigational product or any of its components; * have any ocular condition that, in the opinion of the investigator, could affect the subject's safety or trial parameters (including but not limited to narrow angle glaucoma, clinically significant blepharitis, follicular conjunctivitis, iritis, or pterygium); * have had ocular surgical intervention within 3 months prior to initiating the study or during the study and/or a history of refractive surgery within the past 6 months; * have a known history of retinal detachment, diabetic retinopathy, or active retinal disease; * have the presence of an active ocular infection (bacterial, viral or fungal) or positive history of an ocular herpetic infection at any visit; * use any of the disallowed medications during the period indicated prior to and during the study; * have any significant illness (e.g. any autoimmune disease requiring therapy, severe cardiovascular disease \[including arrhythmias\]) the investigator feels could be expected to interfere with the subject's health or with the study parameters and/or put the subject at any unnecessary risk (includes but is not limited to: poorly controlled hypertension or poorly controlled diabetes, a history of status asthmaticus, organ transplants, a known history of persistent moderate or severe asthma, or a known history of moderate to severe allergic asthmatic reactions to any of the study allergens); * manifest signs or symptoms of clinically active allergic conjunctivitis in either eye at the screening visit; * have planned surgery (ocular or systemic) during the trial period or within 30 days after; * have used an investigational drug or medical device within 30 days of the study or be concurrently enrolled in another investigational product trial; * be a female who is currently pregnant, planning a pregnancy, or lactating. * have cancer or have a history of cancer within the last 5 years.